#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>

int walk(int n)
{
    if (n <= 2)
    {
        return n;
    }
    else if (n > 2)
    {
        return walk(n - 1) + walk(n - 2);
    }
}

int main()
{
    int n = 0;
    scanf("%d", &n);
    int ret = walk(n);
    printf("%d", ret);
    return 0;
}